Solid Electrolytic Capacitor and Method for Producing the Same

Abstract

The present invention relates to a method for producing a solid electrolytic capacitor in which a solid electrolyte layer is provided by a process comprising a step of dipping a valve-acting metal having thereon a dielectric film layer in a monomer-containing solution, followed by drying (Step 1), a step of dipping the valve-acting metal in an oxidizing agent-containing solution, followed by drying (Step 2), and a step of dipping the. valve-acting metal in an oxidizing agent-free solution, followed by drying (Step 3); and to a solid electrolytic capacitor produced thereof. According to the present invention, a thin capacitor element with reduced failure of short circuit and less fluctuation in the element shape can be stably produced, the number of capacitor elements stacked in a solid electrolytic capacitor chip can be increased to realize high capacitance, and a solid electrolytic capacitor element suitable for a solid electrolytic multilayer capacitor with less fluctuation in the equivalent series resistance can be provided.

Description

CROSS REFERENCE TO THE RELATED APPLICATIONS [0001] This is an application filed pursuant to 35 U.S.C. Section 111(a) with claiming the benefit of U.S. Provisional Application Ser. No. 60 / 631,988 filed Dec. 1, 2004 under the provision of 35 U.S.C. Section 111(b), pursuant to 35 U.S.C. Section 119(e)(1).TECHNICAL FIELD [0002] The present invention relates to a solid electrolytic capacitor using an electrically conducting polymer as the solid electrolyte layer, and a production method thereof. BACKGROUND ART [0003] The basic element of a solid electrolytic capacitor is generally produced, as shown in FIG. 1, by forming a dielectric oxide film layer (2) on an anode substrate (1) comprising a metal foil subjected to an etching treatment to have a large specific surface area, forming a solid semiconductor layer (hereinafter referred to as a “solid electrolyte”) (4) as a counter electrode on the outer side of the dielectric oxide layer, and preferably further forming thereon an electricall...

AI Technical Summary

Benefits of technology

[0009] Accordingly, an object of the present invention is to solve those problems, that is, to stably produce a thin capacitor element without increasing short circuit failures while ensuring less fluctuation in the element shape, achieve high capacitance by increasing the number of capacitor elements stacked in a solid electrolytic capacitor chip, and provide a solid electrolytic multilayer capacitor element with less fluctuation in the equivalent series resistance and a production method thereof.

[0010] The present inventors have made intensive studies in the light of the above-described object, as a result, they have found that in the method of forming a solid electrolyte layer by polymerizing a monomer with use of an oxidizing agent on a dielectric film formed on a valve-acting metal surface having fine pores, adding a step of dipping the valve-acting metal in an oxidizing agent-free solution (hereinafter simply referred to as Step 3) to the conventionally known steps of dipping the valve-acting metal in a monomer-containing solution (hereinafter simply referred to as Step 1) and dipping the valve-acting metal in an oxidizing agent-containing suspension (hereinafter simply referred to as Step 2) can greatly narrow the gap (space) between polymer layers having a layer structure and thereby enable to form a dense solid electrolyte with excellent shape stability. The present invention has been accomplished based on this finding.

[0012] The solid electrolytic capacitor obtained in this way is confirmed to be enhanced in the adhesive property of the solid electrolyte formed on the dielectric film and assured of high capacitance and reduction in the dielectric loss (tan δ), leakage current and defective ratio.

[0013] Furthermore, it is confirmed that downsizing and high capacitance of a capacitor can be realized by stacking a plurality of the above-described solid electrolytic capacitor elements having excellent properties.

Problems solved by technology

If the polymerization conditions of the electrically conducting polymer in the cathode portion of the capacitor element are not precisely controlled, the thickness of the electrically conducting polymer becomes uneven and the electrically conducting polymer comes to have a thin portion, in which direct contact of the paste or the like with the dielectric oxide film layer readily occurs, giving rise to increase in the leakage current.

Furthermore, since the number of capacitor elements which can be stacked in a solid electrolytic capacitor chip having a predetermined size is limited by the thickness of the element, the capacitance of the solid electrolytic capacitor chip cannot be increased.

In addition, if the coverage thickness of the electrically conducting polymer is not uniform, the contact area between a capacitor element and a capacitor element stacked decreases and this causes a problem that the equivalent series resistance (ESR) becomes large.

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